The invention is in the field of electronic reproduction technology and is directed to a method and to an apparatus for pixel-by-pixel and line-by-line, opto-electronic scanning of masters chucked on a scanner drum. Such a drum scanner device, referred to below as a drum scanner, can be designed for scanning black-and-white or chromatic masters in reflected light and/or transmitted light.
A drum scanner for scanning transparency masters is composed, for example, of a rotating, transparent scanner drum on which a transparency master to be scanned is chucked, of a light source for the pixel-by-pixel illumination of the transparency master and of a scanner element having a scanner objective, a scanner diaphragm and an opto-electronic transducer for converting the scan light the transparency master allows to pass into an image signal, which represents the luminance values of the scanned picture elements.
The light required for the pixel-by-pixel illumination of the transparency master is transported, for example, from a light source located outside the scanner drum through a light conductor into the hollow-cylindrical interior of the scanner drum, and is imaged thereat onto the transparency master as an illumination spot with a matching objective and a deflection mirror. The scan light modulated with the image content of the transparency master proceeds through the scanner objective into the scanner element located outside the scanner drum and is converted thereat into an image signal by opto-electronic conversion.
The scanner element on the one hand and the optical elements on the other hand are respectively secured to an arm of a U-shaped feed support, whereby the arm carrying the optical elements projects into the scanner drum at the end face.
For planar scanning of the transparency master, the feed support moves in the axial direction of the rotating scanner drum.
In order to be able to scan originals having different formats, the scope of a drum scanner usually includes scanner drums with different diameters that are chucked in the drum scanner dependent on the format of the master to be scanned.
In order to achieve a good scanning quality, an optimum illumination of the masters is required, particularly given employment of scanner drums having different diameters. For optimum setting of the size of the illumination spot on the respective master, lens systems must be manually replaced at the feed support given a traditional drum scanner in order to compensate the different radial distances between the central arm of the feed support and the generated surface of the respective scanner drum, this being relatively complicated.
It is therefore an object of the invention to improve a method and an apparatus for pixel-by-pixel and line-by-line, opto-electronic scanning of masters chucked on scanner drums such that an optimum pixel-by-pixel illumination of the masters is achieved in a simple way and automatically to the farthest-reaching extent, particularly given employment of scanner drums having different diameters.
According to the method of the present invention for point-by-point and line-by-line, opto-electronic scanning of a master, the master is chucked on a scanner drum. A light spot is generated for pixel-by-pixel illumination of the master, the light spot being imaged onto the master as an illumination spot. The scan light is modulated with a content of the master, is focused with a scanner objective, and is converted into an image signal in an opto-electronic scanner element. A feed motion is executed with the illumination spot, scanner objective, and scanner element in a direction of the rotational axis of the scanner drum for scanning of the master. Illuminance of the illumination spot is measured. The illumination of the master is set dependent on the measured luminance by modifying an imaging scale with which the light spot is imaged onto the master as the illumination spot.